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    <title>ShellCheck: SC3014 – In POSIX sh, `==` in place of `=` is undefined.</title>
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    <h1>SC3014 – ShellCheck Wiki</h1>
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    <h2 id="in-posix-sh--in-place-of--is-undefined">In POSIX sh,
<code>==</code> in place of <code>=</code> is undefined.</h2>
<p>(or "In dash, ... is not supported." when using
<code>dash</code>)</p>
<h3 id="problematic-code">Problematic code:</h3>
<div class="sourceCode" id="cb1"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb1-1"><a href="SC3014.html#cb1-1" aria-hidden="true" tabindex="-1"></a><span class="co">#!/bin/sh</span></span>
<span id="cb1-2"><a href="SC3014.html#cb1-2" aria-hidden="true" tabindex="-1"></a><span class="cf">if</span> <span class="bu">[</span> <span class="va">$1</span> <span class="ot">==</span> <span class="st">&quot;-n&quot;</span> <span class="bu">]</span></span>
<span id="cb1-3"><a href="SC3014.html#cb1-3" aria-hidden="true" tabindex="-1"></a><span class="cf">then</span></span>
<span id="cb1-4"><a href="SC3014.html#cb1-4" aria-hidden="true" tabindex="-1"></a>  <span class="va">dry_run</span><span class="op">=</span>1</span>
<span id="cb1-5"><a href="SC3014.html#cb1-5" aria-hidden="true" tabindex="-1"></a><span class="cf">fi</span></span></code></pre></div>
<h3 id="correct-code">Correct code:</h3>
<div class="sourceCode" id="cb2"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb2-1"><a href="SC3014.html#cb2-1" aria-hidden="true" tabindex="-1"></a><span class="co">#!/bin/sh</span></span>
<span id="cb2-2"><a href="SC3014.html#cb2-2" aria-hidden="true" tabindex="-1"></a><span class="cf">if</span> <span class="bu">[</span> <span class="va">$1</span> <span class="ot">=</span> <span class="st">&quot;-n&quot;</span> <span class="bu">]</span></span>
<span id="cb2-3"><a href="SC3014.html#cb2-3" aria-hidden="true" tabindex="-1"></a><span class="cf">then</span></span>
<span id="cb2-4"><a href="SC3014.html#cb2-4" aria-hidden="true" tabindex="-1"></a>  <span class="va">dry_run</span><span class="op">=</span>1</span>
<span id="cb2-5"><a href="SC3014.html#cb2-5" aria-hidden="true" tabindex="-1"></a><span class="cf">fi</span></span></code></pre></div>
<h3 id="rationale">Rationale:</h3>
<p><code>==</code> is used for equality comparison in C-like languages,
and is also supported by <code>bash</code> and <code>ksh</code> in
<code>[ .. ]</code> and <code>test</code> expressions.</p>
<p><code>sh</code> and <code>dash</code> only supports <code>=</code>
for equality comparison, so use that instead.</p>
<h3 id="exceptions">Exceptions:</h3>
<p>If you only intend to target shells that supports this feature, you
can change the shebang to a shell that guarantees support, or <a
href="ignore.html">ignore</a> this warning.</p>
<p>You can use <code># shellcheck disable=SC3000-SC4000</code> to ignore
all such compatibility warnings.</p>
<h3 id="related-resources">Related resources:</h3>
<ul>
<li>Greg's Wiki
<ul>
<li><a href="https://mywiki.wooledge.org/BashPitfalls#pf20">Bash Pitfall
#20: <code>[ bar == "$foo" ]</code></a></li>
<li><a href="https://mywiki.wooledge.org/Bashism#Conditionals">Bashism -
Conditionals</a></li>
</ul></li>
</ul>
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